Note: Descriptions are shown in the official language in which they were submitted.
CA 02257205 1998-12-02
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20902 PCT/DE97/01299 Transl. of PCT/DE97/01299
DESCRIPTION
FR08TH$TIC HHART VALVB
The invention relates to a prosthetic heart valve comprised
of a supporting housing (stent) to which one or more flexible or
rigid cusps and a suture ring are fastened. Simultaneously, the
invention relates to biprosthesis or mechanical valves with a
support housing to which a suture ring is affixed. The heart valve
known, for example, from DE 38 34 545 C2 is comprised of a support
housing composed a cylindrical base ring which is provided along
its periphery with three axially tapering posts [stays] offset
about the periphery respectively by 120°. The wall end facets
lying between the posts serve to take up and secure three cusps
[leaflets] which insure the closing and opening of the heart valve.
In the closed state, the cusps [leaflets] lie against one another
along their free ends and form together in overlapping region.
Apart from the aforedescribed aortic valve, so-called mitral valves
are known which instead of having three cusps [leaflets], have only
two cusps [leaflets].
So that the heart valve is well matched to the annulus
and can be fastened in place, prosthetic heart valves have suture
rings which are affixed on the outer periphery of the housing,
approximately at the level of the inflow plane. The suture ring
can be sutured after implantation with the tissue of the patient in
order to anchor the prosthetic heart valve fixedly in its implanted
position.
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EP 0 443 993 B1, as has already been indicated, discloses
suture rings which are coated or completely formed of a
biocompatible synthetic tissue and have the advantage that the
slidability for the needles and the stitching threads can be
improved, thereby simplifying the suturing into the annulus tissue
although with the drawback that blood absorbing, hemolytic or
thrombogenic effects can result. To avoid these, a liquid repellent
material, like for example, polytetrafluoroethylene (Teflon) can be
used. The use of such liquid repellent materials, however, is
contradictory to the requirement that the outer region of the
suture ring enable growth into the patient tissue. In order to
satisfy these different requirements, according to the afore-
mentioned patent, the suture ring can be comprised of a composite
body of two materials, of which the first is substantially
hemocompatible so that it does not absorb substantially any blood
and has a reduced hemolytic and thrombogenic effect, while the
second material is substantially hydrophilic and porous so that
growth into the patient tissue is promoted. The first material is
applied on the respective end sides of the suture ring and the
second material on the peripheral surface. A drawback of this
construction of such a suture ring is that it is expensive and is
only limitedly satisfactory from the point of view of the shear
forces or torsion forces which arise with respect to insufficient
stability.
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In EP 0 443 994 B1, a suture ring is proposed
which has a core and an internal edge bead engaged in a
groove of the outer wall of the support housing. Outwardly
of this engagement region, the suture ring is provided with
a coating which is so obtained that the contact between this
coating and support housing outer wall surfaces insures a
sufficiently great resistance against relative rotation of
the suture ring and the support housing. This suture ring
also has the aforedescribed drawbacks.
Further core-sheath restructures of the suture
ring have already been described for example in
EP 0 119 357 A1, in EP 0 075 530 A1, in GB 2 021 530 A1 and
in EP 0 145 166 A2. In the last-mentioned publication, the
core ring is comprised of a memory alloy which is so
selected and treated that the body temperature of the
patient generates a core-ring contraction which gives rise
to a sufficient clamping force effect.
DE-A 1 180 087 describes a heart valve prosthesis
with a valve body, a valve member movable relative to the
valve body and a fixing ring serving for attachment of the
prosthesis which is formed as an independent component and
is connectable with the valve body. The connection of the
valve body and the fixing can either be nonreleasable, for
example, by cementing or welding, or releaseable, for
example by a form connection or plug connection of a
bayonette joint. The part of the fixing ring remote from
the valve body is encased with a coarse, mesh synthetic
fabric, for example, knit polytetrafluoroethylene which is
rolled up into a loose cushion and with the aid of a strong
thread is held together.
A broad aspect of the invention provides
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a prosthetic heart valve comprised of a support housing to
which at least one cusp and a suture ring are fastened,
characterized in that the suture ring is cemented by an
adhesive to the support housing, wherein the suture ring,
the at least one cusp and outer surfaces of the support
housing are composed of the same material.
Another broad aspect of the invention provides a
process of producing the prosthetic heart valve as
aforesaid, characterized in that a suture ring blank is
prefabricated by injecting a suture ring material, upon a
substantially planar surface like a glass plate or on a hose
cylinder shell and then the suture ring blank is cut or
stamped to the suture ring of a desired size, before the
suture ring is cemented to the support housing, and in that
the outer surfaces of the support housing, the at least one
cusp and the suture ring are made of the same material.
A further broad aspect of the invention provides a
process for producing the prosthetic heart valve as
aforesaid, characterized in that the suture ring is injected
directly in a desired width and thickness on the support
housing and in that the outer surfaces of the support
housing, the at least one cusp and the suture ring are made
of the same material.
It is the object of the present invention to
provide a prosthetic heart valve of the originally mentioned
type, whose suture ring is securely affixed on the outer
wall of the support housing, whereby the suture ring has a
sufficient slidability for the needle and thread used to
suture the ring in the annulus, as well as a sufficient
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flexibility. The suture ring structure should, finally, be
suitable for growth with the body tissue of the patient.
By contradistinction to the known connections up
to now according to the state of the art, which rely upon a
force or friction connection or a form-fitting setting
arrangement or a combination of two, with an adhesive
bonding, not only is a reliable, durable fixation of the
suture ring on the heart valve support housing effected, but
also the suture ring construction is simplified and can be
of suitable biocompatible material. Because of the
condition which can be assured that the adhesive which is
used will not come into contact with the patients' tissue or
the patients' blood, practically any adhesive known from the
state of the art, for example, an epoxy resin, can be used.
According to a feature of the invention, however,
the adhesive material is the same material, preferably
polyurethane, as is used to also comprise the support
housing and/or the suture ring. If, for example, the cusps
[leaflets] are also composed of polyurethane, the entire
heart valve can be fabricated from a single material which
effectively avoids material stresses especially as a
consequence of different thermal expansion coefficients
(before, during and after implantation).
According to a further feature of the invention,
the adhesive bond between the suture ring and the support
housing is sealed toward the exterior, i.e, at the
interfacial edges.
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The suture ring is comprised preferably from a
microporous, fine fibrillar structure which promotes growth with
the intrinsic body tissue of the patient. If necessary or if
desired, a local intergrowth with intrinsic body tissue of the
patient can be targeted at certain locations of the suture ring by
sealing (coating) at areas targeted for suppression, for example,
to hinder the growth of tissue into the inflow cross section.
According to the invention, a number of processes are
available for production of the aforedescribed new heart valve.
In a first process variant, a suture ring blank is
prefabricated by spraying the suture ring material which preferably
is comprised of polyurethane, on a glass plate or a hose cylinder
wall. This suture ring blank is then cut or stamped to a desired
suture ring size and suture ring shape after removal from the glass
plate or the hose cylinder wall, before the finished suture ring is
cemented to the support housing.
The cementing can be effected in that adhesive is coated
onto the support housing wall outer surface which is provided and
the suture ring is then shoved onto the adhesive coated surface,
positioned and the adhesive permitted to dry.
Alternatively thereto, it is possible to shove the
prefabricated suture ring onto the support housing surface which is
provided, to orient the suture ring and then to lift the inner wall
of the suture ring around the support housing at least at several
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locations therefrom and to fill adhesive into the
intervening space before the adhesive is dried. It is also
possible to apply the adhesive, after the suture ring has
been shoved onto the support housing surface and oriented
thereon, by means of a cannula at the common contact surface
of the suture ring and the support housing by injection of
the adhesive, and allowing the adhesive to dry. In this
possible variant of the method, before the suture ring is
shoved onto the support housing surface, the latter can be
sprayed or coated with adhesive to yield a first adhesive
layer thereon.
An alternative fabrication of the prosthetic heart
valve is described, whereby the suture ring is directly
injected [sprayed] with the desired width and thickness on
the support housing. In this case, preferably around the
annular surface which is provided to receive the suture
ring, the remainder of the supporting housing is masked by
injection [spraying] so that only in the region of the
supporting housing that the suture ring application is to
occur can such an application be applied. The masking
material for the remainder of the support housing at least
at the edge which is to define the free annular surface of
the suture ring, has a thickness which corresponds to the
desired sutured ring thickness.
If one selects, as has already been indicated
above, a material for the suture ring which is the same
material as for the support housing, especially
polyurethane, be appropriate practice
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of the process, a stable cross linking can be achieved at the
bonding locations of the suture ring with the support housing so
that a unitary body of a single material is obtained with a simple
suture ring construction.
Embodiments of the invention are shown in the drawing.
It shows:
FIG. 1 a perspective view of a three-cusp aortic valve
(without suture ring),
FIG. 2 a section along the plane A-A in FIG.1,
FIG. 3 a perspective view of a two-cusp mitral valve
(without suture ring),
FIG. 4 a section along the line B-B in FIG. 3,
FIG. 5 a perspective view of a further mitral valve, and
FIG. 6 is a plan view of the mitral valve according to
FIG. 5 without suture ring.
The heart valve shown in FIGS. 1 and 2 is comprised
substantially of a support housing 10 with three cusps [leaflets]
11 which are affixed on the radially outwardly disposed inclined
surfaces, namely, the end surfaces 12; of the wall 13 of the
support housing. The support housing 10 has a base ring 14 whose
diameter determines the valve throughput and is rounded at its
inner wall edge in the inlet region. The wall 13 is substantially
perpendicular to the base ring ground surface, whereby three tips
15 project as posts at an angular offset of 120° from one another
and between which the end face 12 of the wall 13 runs in circular
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arc form. The inner edges of these end surfaces 12 between two
posts lies in a respective plane which is defined as an
intersection of a cylinder with a plane inclined to its
longitudinal axis as a result, an angle of attack of the three
planes of about 8~0° relative to the base ring ground surface
results. The support housing is comprised of elastic synthetic
resin. It can be a thermoplast like polyamide which is produced,
for example, by injection molding and can be coated with
polyurethane after roughening of the surface. The cusps 11
[leaflets] are comprised of a flexible thin synthetic resin foil
which preferably also are fabricated from polyurethane. The wall
13 has an outer smooth and straight portion and serves as is
visible from FIG. 2 to enable a suture ring 16, which has a
substantially hollow cylindrical form, to be affixed thereto, the
suture ring 16 having on its two end edges, ring-shaped beads.
This suture ring material is also comprised of polyurethane.
To fabricate the aorta valve illustrated, the support
housing 10 is injection molded and is initially provided with the
three cusps 11 [leaflets] which can be cemented on the end surfaces
12. The cusps [leaflets] themselves have been previously cut from
a planar polyurethane foil. Then, either the already prefabricated
suture ring is cemented onto the support housing outer wall in the
region of the base ring 14 or injected directly onto the latter.
In the first case, the suture ring is initially injected onto a
glass plate or hose-shaped cylindrical body from a fleece with
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microporous fine fibrillar structure. After cutting of the
prefabricated part into the desired suture ring shape and sealing
possible cut edges were desired, the suture ring is pressed onto
the outer wall of the support housing 10 at the level of the base
ring 14, is oriented there and then adhesive is injected between
the suture ring and the support housing 10. Alternatively or
additionally, before the suture ring 16 is pressed onto the
carrying surface and oriented thereon, this region can be coated
with adhesive. In a treatment variant, the side turned toward the
flow and the side turned away from the flow of the transition zone
between the suture ring 16 and the outer wall of the support
housing 10, can be annularly sealed with adhesive.
The mitral heart valve illustrated in FIGS. 3 and 4 is
comprised of a support housing 20 with two cusps [leaflets] 21 and
a suture ring 22 which is affixed along the outer wall at the level
of the inlet region of the support housing 20. The one piece
support housing 20 has a base ring 23 whose inner edges in the
inlet region are rounded in a manner known from the state of the
art. The wall 24 which extends substantially perpendicular to the
base ring ground surface, is subdivided into a first wall with
reduced curvature and a second wall with greater curvature which
together in plan view onto the base ground surface, define two
semi-ellipses with a common longitudinal axes. The half
transverse axes can be of different length, preferably with a
length ratio of 1:2. The upper end surface 26 of the wall 24
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serves as a fastening surface for the cusps [leaflets] 21. Each
of the two end surfaces 26 between two posts 25 has an inner edge
at an inclination to the base ring ground surface which forms the
inlet region. In the present case, the connecting lines between
the cusps [leaflets] 21 and the upper inner edges of the wall 24
each lie in a plane which runs at an angle of about 50° or about
35° with respect to the base ring ground surface. The cusp
settings are therefore different. The posts 25 have a prismatic
contour and widen uniformly to their upper end surfaces 27 which
are substantially triangular. In a plan view of the inner wall of
the support housing 10 (see FIG., 4) it can be seen that the posts
are V-shaped and end in a wedge configuration above the base ring
base surface in the inlet region of the support housing 10. The
cross sections of the posts 25 parallel to the base ring ground
surface forms a substantially equilateral triangle. The post axes
28 are not vertical relative to the base ring ground surfaces, but
are slightly inclined with respect to surface normals, especially
with an angle of 15°. A corresponding inclination is shown by the
end face 27 of the post [stay] relative to the base ring ground
surface. The posts 25 replace the commissure regions of the
natural heart valve and serve as prismatic inner seats for the
cusps [leaflets] 21 with their unilateral triangular shanks.
A further form of mitral valve is shown in FIG. 5. In
contradistinction to the mitral valve shown in FIGS. 3 and 4, the
posts in the walling 30 are integrated with equal thickness. In
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the regions of the aforedescribed posts, the wall has its greatest
height, measured from the base ring, and ends either at an acute
angle or as has been shown in FIGS. 5 and 6, in a flattening 31.
The posts do not extend any longer geometrically "out of the
walls". The walling 30 is thicker between the two post regions
than in the remainder of the posts (see reference character 31).
In contradistinction to the suture ring shown in FIG. 2,
the suture ring 22 according to FIG. 4, on anatomical grounds, for
reducing the suturing stresses, is wide edged and in the form~of a
suturing cap. This so-called super annular construction is
preferred for mitral heart valves. The fastening of the suturing
22 corresponds to that described previously with respect to the
aorta valve.
The advantages of the fleece-like suture rings of
polyurethane which are used lie in their good surgical
manipulability with respect to the smoothness of the material upon
suturing. It is also possible to process the suture ring already
affixed to the support housing prior to the implantation by cutting
in order to insure a better match in the annulus of the patient.
The polyurethane suture ring has a good wear resistance and a high
elasticity. Furthermore, the polyurethane suture ring is also
characterized by good hemocompatability. Because of the
microfibrillar structure, a rapid and above a control healing with
surrounding tissue of the patient is possible. There is only a
very thin formation of neointima, a formation of giant cells and
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excessive pannus are avoided. Thromboambolytic complications are
also reduced as is the risk of perivalvular leaks and endocarditis.
The tissue tolerance of the suture ring is good.
A further advantage resides in that the entire valve can
be comprised on its surface of the same material. The fabrication
and bonding of the suture ring to the stent is simplified and a
large number of steps is not required. The number of elements
which must be used is small and the elastic structure of the suture
ring gives rise to a secure fixation of the suture ring wherever it
lies in contact with the support housing. The process of the
invention enables production of a suitable prosthesis (fabrication
of the support housing with cusps [leaflets]) separately and a
reduced cost for the production of the suture ring and it is
relative simple assembly of the suture ring with the support
housing by cementing.
In the fabrication of the described heart valve, the
cusps [leaflets] which have been previously formed can be affixed
by cementing or welding onto the end surfaces of the support
housing. Alternatively, it is also possible to fabricate the heart
valve by the injection molding technique known from the art,
including two component injection, in which initially the support
housing is made and then the cusps [leaflets] are applied by
injection molding. A further possibility is the use of so-called
immersion technique. In this process the support housing which may
be made from polyamide, after a coating with polyurethane can be
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shoved onto a corresponding mandrel having forming surfaces for the
cusps [leaflets] and the mandrel with the support housing is
immersed in a liquid synthetic resin solution (polyurethane) and
tumbled therein until the desired thickness distributions is
reached. During the tumbling, the synthetic resin hardens.
On the thus fabricated unit of support housing and cusp
or cusps [leaflets], the suture ring is fastened in the above-
described manner.
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